1. Field of the Invention
The present invention relates to a desiccant assisted air conditioning apparatus utilizing a heat pump device for desiccant regeneration and cooling of process air.
2. Description of the Related Art
Desiccant assisted air conditioning apparatus is well known, for example in a U.S. Pat. No. 2,700,537. The reference discloses a desiccant assisted air conditioning apparatus requiring a heat source of a temperature range of 100-150.degree. C. for regenerating the desiccant (moisture adsorbent), such as electric heaters or boilers. In recent years, desiccants which can be regenerated at lower temperatures in a range of 60-80.degree. C. have been developed so that heat sources operating at lower temperatures can be utilized.
FIG. 6 is a schematic representation of a typical example of such improved desiccant assisted apparatus, and FIG. 7 is a psychrometric chart showing the operation of this example apparatus. In FIG. 6, the reference numeral 101 refers to a conditioning space; 102 refers to a blower; 103 refers to a desiccant wheel; 104 refers to a sensible heat exchanger; 105 refers to a humidifier; 106 refers to a water supply pipe for the humidifier; 107-111 refer to air passages for conditioned air flows; 130 refers to a blower for the regeneration air; 120 refers to a heat exchanger between hot water and regeneration air (hot water heat exchanger); 121 refers to a sensible heat exchanger; 122, 123 refer to hot water passages; and 124-129 refer to air passages for regeneration air. In FIG. 6, circled letters K-V represent thermodynamic states of the air corresponding to respective sites shown in FIG. 7, SA designates supply air, RA designates return air, OA designates outside air and EX designates exhaust air.
In the above desiccant assisted air conditioning apparatus, after dehumidifying the return air (process air) through moisture adsorption process by flowing it through the desiccant wheel 103, the return air is cooled by heat exchange with the regeneration air, and is supplied to the conditioning space. In the meanwhile, outside air is used as regeneration air, which is heated by a heat transfer medium of an external heat source (not shown) and is introduced to the desiccant wheel 103 for regenerating the desiccant wheel 103. The regeneration air is exhausted to the outside environment. The conditioning space is cooled by repeating the above processes.
One of the alternatives of the above apparatus utilizes exhaust air from the conditioning room as regeneration air and introduces the outer air as a process air.
The energy efficiency of such an air conditioning apparatus is given by a value of coefficient of performance (COP=.DELTA.Q/.DELTA.H) which is obtained by dividing the enthalpy difference .DELTA.Q (an indication of cooling effect) shown in FIG. 7 by regeneration heat .DELTA.H (amount of the regeneration heat). In the conventional desiccant assisted air conditioning apparatus, even though the temperature of the hot water required for heating the regeneration air has been lowered compared with the earlier apparatus, the COP values are still lower than those of air conditioning apparatus which uses other thermally driven refrigeration devices, such as a double effect absorption chiller for cooling and dehumidification of ambient air. The reason is that, though it is based on a high temperature heat source of a boiler, the system only utilizes less than one unit of high quality energy (excergy) out of one unit at temperatures less than 100.degree. C. for the regeneration of the desiccant.
One of the measures to solve the above problem is an air conditioning apparatus, as shown in FIG. 8, in which an absorption heat pump 200, in place of a boiler, is provided as a heat source. The heat recovered from an absorber 1 and a condenser 4 is introduced to the heater 120 through the heat transfer medium passages 123, 42, 43, 122, and the cooling effect generated in the evaporator 3 is introduced into a cooler 115 provided in the process air passage through refrigerant passages 118, 53, 117. According to the air conditioning apparatus, a cooling effect due to a sensible heat exchange between the process air and the regeneration air (.DELTA.Q-.DELTA.q) can be obtained in addition to the cooling effect (.DELTA.q) of an absorption heat pump 200 so as to realize a higher energy efficiency with a more compact construction of the system than the air conditioning system shown in FIG. 6.
However, in the air conditioning device described above, when an absorption refrigeration cycle of a so-called single effect type is used in the absorption heat pump, and a lithium bromide-water working fluid system is used, if the absorption temperature is set 60-80.degree. C., which is suitable for a heat source of the desiccant assisted air conditioning apparatus, while the evaporation temperature is set 10-15.degree. C., which is suitable for cooling temperature of the process air, then the thermodynamics state of the absorbent fluid compatible with such liquid temperature and evaporation pressure condition exceeds a crystallization limit so as to disable the operation due to crystallization. Also, since the condensation temperature is raised to 60-80.degree. C., the difference between the temperature of the condensed refrigerant and the evaporation temperature (10-15.degree. C.), and, consequently, the difference in enthalpy therebetween are increased. As a result, the cooling efficiency is much lowered compared to ordinary absorption chiller, where condensing temperature is approximately 40.degree. C., due to the self-evaporation of the refrigerant when it is introduced into the evaporator, so that the COP value of the heat pump is deteriorated.